Body language is like a picture frame. People make judgements about the artwork - even though it may be quite good - by the type of frame you put it in. You want your picture frame to be good so people can appreciate the artwork inside (your speech).
What is good body language? We want to be able to express ourselves flexibly rather than be stuck in a static pose but there are some general things to look out for:
(In true Andy fashion, those letters make up the vowels of the alphabet backwards. If I think of a better one I'll re-do this.)
To get a sense of these think of something you really like. Let's say it's ice cream.
Get into a position exactly opposite all the things listed above. Take a posture that's collapsed and look down at the ground. Close your arms and hands tightly around yourself. Finally, put a frown on, a real scowl.
Now say "I like ice cream" (or whatever the thing you really like is). It doesn't feel right, does it?
Now let your posture open upwards, no longer looking at the floor, and say it again: “I like ice cream”. It should feel slightly better.
Uncross your arms and say it again. Check how you feel.
Now add a smile and say it again. Check how you feel.
By this time, you probably feel a lot more like you do indeed like ice cream (or, again, your individual thing).
One last thing: keep your upward and open posture with your smile but this time deliberately tense up and contract every muscle you can. Keep your smile but every other facial muscle contracts. Then say "I like ice cream". I bet now it's back at least partially to not really feeling like you do.
Finally, keep your open and upward posture along with your smile and relax. One last time, say it: "I like ice cream!" (This is to re-set you back to positive.)
The feeling we ended with is the feeling you want. It's not any particular thing but it's generally up, open and interested. Into that frame you can put any picture you want to convey to the audience.
As a side effect, you'll also feel better about yourself when you are giving your speech.
People can be divided into three groups in relation to the use of gestures in public speaking.
Interestingly enough, one is the chronic gesturer. He or she cannot speak without using their hands. If you think of some cultures that are stereotyped as speaking that way, you get the idea. To address this:
The two other groups are: those people who are stuck in a pose (e.g. hands in pockets or hands clasped in front of them) or those people who are stuck except for one part of their body that is fidgeting (like a hand or a foot twitching). A variation of the fidgeting is holding onto the podium or lectern for dear life to suppress your desire to fidget.
Finally for all three groups, learn to walk away from the podium or lectern. In one speech, go outside the boundaries a little. Next speech, separate yourself from the podium for part of your speech (deliver it to one corner of the room). For the speech after that, try not to go near the podium at all.